<mat-form-field>
  <mat-select placeholder="Panel color" [formControl]="panelColor"
              panelClass="example-panel-{{panelColor.value}}">
    <mat-option value="red">Red</mat-option>
    <mat-option value="green">Green</mat-option>
    <mat-option value="blue">Blue</mat-option>
  </mat-select>
</mat-form-field>
